| Popis: |
The compounds 18- and 19-trideutero-11-cis-retinal, > 99% pure, with over 98% and 99% trideuterium incorporation were synthesized together with the corresponding all-trans derivatives. Rhodopsins were prepared from bovine opsin and 18- and 19-trideutero-11-cis-retinal. 18- and 19-trideutero-all-trans-retinal were isolated as oximes after photolysis of the corresponding rhodopsins. The oximes showed the same deuterium incorporation as the starting 18- and 19-trideutero-11-cis-retinals and as those oximes obtained by denaturation of 18- and 19-trideuterorhodopsin in the dark. These results demonstrate that during rhodopsin photolysis no detectable exchange of D or H occurs at carbon atoms 18 and 19. These facts, together with Resonance Raman data of 18-trideutero-bathorhodopsin and 5-demethyl-bathorhodopsin, establish that the primary step in rhodopsin photochemistry is not a phototautomerization involving the 5-CH3 group. With respect to the possibility that the primary step is a phototautomerization involving the 9-CH3 group, the situation is less clear. At this time tile experimental evidence of the various research disciplines is insufficiently conclusive to establish unambiguously which of the two possibilities, cis-trans photoisomerization or phototautomerization involving the 9-CH3 group, is the primary event in visual photochemistry. |
